There is a demand for technology that can generate hydrogen of a high purity and supply it in a stable manner as fuel for a fuel cell. Steam reforming of hydrocarbon gas is an example of a known method for generating hydrogen. But in such steam reforming of hydrocarbon gas, when the mole ratio of steam to raw material becomes low, coking of the carbon on the catalyst occurs, which deactivates the catalyst. The production conditions must therefore be carefully controlled corresponding to the amount of hydrogen to be produced.
Another known method for generating hydrogen is to decompose ammonia using a catalyst. However, although it is possible to generate hydrogen from decomposed ammonia when using such an ammonia-decomposing catalyst, it is not possible to separate the hydrogen from the mixed gas consisting of ammonia, hydrogen, and nitrogen obtained by decomposing the ammonia.
The inventors invented a method and apparatus for generating hydrogen by transforming ammonia into plasma by electric discharge, which is disclosed in Patent Document 1. Patent Document 1 discloses a hydrogen generating apparatus including a plasma reactor, a high-voltage electrode, and a grounding electrode. In the hydrogen generating apparatus of Patent Document 1, a hydrogen separation membrane functions as the high-voltage electrode, which causes a dielectric barrier discharge between the hydrogen separation membrane and the grounding electrode at room temperature and atmospheric pressure, whereby the ammonia in a feed gas is transformed into plasma to generate high-purity hydrogen. By using the hydrogen separation membrane for electric discharge, separation of high-purity hydrogen from the mixed gas can be performed at room temperature and atmospheric pressure.
In the hydrogen generating apparatus using plasma electric discharge as described in Patent Document 1, it was necessary to increase the electric power for uniform plasma transformation of the raw material in the cylindrical reactor in accordance with the capacity of the reactor. Larger reactors could thus actually be less energy efficient than smaller reactors, which came with a risk of low hydrogen yield and reduced energy efficiency when there was a need for large-scale production of hydrogen.